We have identified a chimpanzee (C499) that developed AIDS and died, approximately 11 years after first being infected with HIV-1. Transfer of virus from this animal (via blood transfusion) to an uninfected chimpanzee (C455) has induced rapid and sustained depletion of CD4+ cells, leading to immunosuppression. Virus derived from C499 was inoculated into two other chimpanzees, one uninfected, the other previously infected with HIV-1. We are currently following the status of these animals. In vitro work with viruses derived from C499 and C455 show that they are quite cytopathic for chimpanzee cells in vitro. We are at present working on developing molecular clones of these viruses and will continue our in vitro analyses of the viruses and of the genetics of viruses isolated from C499 at various times after infection in order to identify the changes associated with development of disease.